Measuring nerve excitation with polarized light.

There are changes in nerve birefringence and optical activity associated with nerve impulses. The birefringence response resembles the time integral of the gating current. Its magnitude suggests several hundred peptide bonds per channel reorient during excitation. The optical activity change has a different time course from the birefringence signal. Its amplitude is approximately consistent with the reorientation of alpha-helices within sodium channel molecules.